This work presents the application of the methodology proposed by Pinto and Alfonsi (1974) for the estimations of the air temperature in the watershed of the Piquiri-Paraná river. This methodology is presented as an alternative for the development of climatological studies in river basins that do not have enough meteorological data. The methodology was applied in the Piquiri-Pr river basin and to test the reliability of the technique, a correlation was made between the estimation method and the temperature observed in four IAPAR meteorological stations, which presented a correlation higher than 0.98. The estimated values were calculated for 73 localities with their respective latitudes and altitudes, pre-established by the Águas do Paraná Institute, and by means of interpolation, isothermal maps were produced with annual and monthly mean. It was observed that the distribution pattern of the highest and lowest mean air temperatures correspond to the values presented by the climatic classification of Köppen (1948), the north of the basin presented the highest temperatures, while the center-south the lowest. The methodological proposal was effective and can be used for other studies such as the climatological water balance, the determination of evapotranspiration and the periods of surplus and water deficiencies in watersheds
